The prostatic acid phosphatase (PAP) is an antigenically specific marker enzyme for prostatic epithelial cells. In order to define the antigenic specificity of PAP in relation to acid phosphatases of other tissue origin, the PAP was dissociated into a subunit polypeptide. The subunit polypeptide (M.W. 50,000) is antigenically similar to the whole molecule. Further studies on the purification of acid phosphatases of other tissue origin and the cleavages of the PAP molecules are in progress. Elaborating various immunoassay methods for this enzyme (counterimmunoelectrophoresis, RIA, EIA, IF, etc.) we are trying to correlate the PAP levels in the biological fluids of the PAP-synthesizing metastatic prostatic carcinoma cells in the biopsy materials with the clinical progression of prostatic carcinoma.